CFD Online Discussion Forums

CFD Online Discussion Forums (
-   CFX (
-   -   Multiphase Multicomponent mass transfer -Initial condition (

pannsave October 20, 2010 13:59

Multiphase Multicomponent mass transfer -Initial condition
Dear CFD users

I have problem with specifying the initial condition of my problem which is basically involves multicomponent with two phases (oil and aqueous phase) mass transfer occurs.

Let me explain my problem clearly

A single domain has initially two phases with oil and aqueous phases and oil phase has soluble of component of A, is going to transfer to aqueous phase when both phases contact.

The oil phase is placed at the top of aqueous phase and is separated by clear boundary. Above this boundary, the oil phase occurs only and below that, aqueous phase occurs

In oil phase region, volume fraction of oil phase is 1 and mass fraction of soluble component “A” is 0.236 and component “B” is 0.764
In aqueous phase region, volume fraction of aqueous phase is 1 and mass fraction of soluble component “A” is 0.0 and component “C” is 1.0

So it is basically muticomponent and mass transfer which occurs between two phases.

Since for multicomponet fluid, we have to define the one of component as constraint.

I defined the organic phase (variable composition mixture) has two component, component A is modeled as transport equation and the component B is treated as constraint.
Similarly, for the aqueous phase (variable composition mixture) has two components, component “A” is modeled as transport equation and the component “C” is treated as constraint.
This is what I was done for setup of initialization of domain.

When I check the initial condition in the CFX post, I noticed that mass fraction of component “C” of aquesous phase shows value of 1 for whole domain.
Similarly, the aquesous phase region (lower part of domain) shows the component “B” of organic phase at the mass fraction of 1,
This is not the case where I set initial condition.

I think these incorrect initial conditions because of consideration of “constraint” of one the component in multicomponet fluid.

Please advise me to setup the correct the initial condition.

Thaks in Advance


joey2007 October 21, 2010 01:07

Multiphase is usually a bit tricky. Possibly the reason can be seen when you post the CCL sections, defining the phase interactions.

pannsave October 21, 2010 04:39

1 Attachment(s)
Dear Joey..

Thanks your reply. I am attaching the ccl of my case.
I would like to see your comment on it



joey2007 October 23, 2010 05:06

CCL says: your component A should be zero everywhere in the water. Clearly the water has 1 within its phase. In the oil it depends on your step function. I would check it pre-evalute the expression in Pre or be an additional variable in post.

pannsave October 23, 2010 06:09

Thanks Joey.
But if you see mass fraction of the component A of water phase in whole domain using cfx post. The contour shows that the upper region (region of oil phase) of domain occupies only componet of A of water phase.
Infact volume fraction of water phase is zero on the upper region.
Have you noticed it..

Once again thanks


joey2007 October 23, 2010 10:55

I do not see your post, even if it wood be nice to have this feature ;)

What did you check? The backup at zero?
I would test the step functions without running the solver. I would use post ad. var. .

pannsave October 23, 2010 15:59

The conditions are fine when using back file at zero.
But if you check after few iterations, you can notice it .

joey2007 October 25, 2010 14:18

Does it change directly after the first iteration or slowly with iterations 2-10?

pannsave October 26, 2010 03:51

It has changed directly after first iteration.

joey2007 October 26, 2010 14:36

If backup at zero is ok, then the solve initializes as you intended. If it is changed after the first iteration, it means that the solver recalculates something. Do not see the reason why. (well I have not so much time to check)

BTW: CCL says its 11. I would use 12.1.

armyou February 9, 2011 02:12

Now, I am also facing such a problem. According to the CFX help, it seems that the sum of the mass fraction of all components should be 1 in the domain. There is no other option.

All times are GMT -4. The time now is 18:01.